Various systems for applying clamping pressure to a pair of mold sections of a molding machine have been disclosed in the patent literature. See for example, United States Letters Patent Nos. 3,104,433 (Hoern), 3,704,973 (Renfrew et al), 4,696,632 (Inaba), 4,710,119 (Otake), 4,929,165 (Inaba et al), 4,968,239 (Inaba et al), 4,966,738 (Inaba et al), and 4,984,980 (Ueno).
Renfrew et al '973 patent discloses the use of an
The electrical induction motor having a shaft to which a nut is secured. The nut meshes with threads of a lead screw so that when the motor is operated, i.e., rotated, the lead screw moves in a first direction to carry one mold section toward the other section to close the sections. An annular cylinder having a hydraulically operated annular piston therein is mounted to the motor with the lead screw extending through the center of the cylinder and with the piston secured to the nut on the lead screw. A pair of annular spaces are provided in the cylinder on either side of the piston. Oil from a high pressure pump or pressure accumulator is injected into one annular space to apply a high clamping force directly on the nut threadedly mounted on the lead screw and carrying the piston, to thereby establish the final closing pressure on the mold sections. Thus, the high clamping force is imposed directly on the nut and lead screw; thereby requiring that they be of a sufficiently large size and of a sufficiently rigid construction to repeatedly withstand the high clamping forces imposed upon them during the mold closing and clamping operations. The introduction of oil into the other annular space effects the initial retraction of the piston and hence the lead screw with it. Thereafter the motor is operated to rotate in the opposite direction to carry the lead screw with it so that the mold sections are separated.
The Ueno '980 patent and the Hoern '433 patent also disclose the use of electric motors to advance mold sections into a substantially closed condition, and thereafter use separate hydraulic cylinders to maintain a clamping pressure of the closed mold sections.
While those patents may be generally suitable for their intended purposes they never the less leave something to be desired from one or more of the following standpoints, simplicity of construction, cost, efficiency and reliability of operation, power consumption.